1. Field of the Invention
The present invention relates to non-invasive devices and methods for measuring and evaluating the absolute and relative muscular strength and the relative coordination of hand digits innervated by the median and ulnar nerves to detect the presence, type and severity of disease. Specifically, the present invention provides a method and apparatus by which the ratiometric strengths and the coordination of the digits may be measured and analyzed to distinguish between repetitive motion injuries such as Carpal Tunnel Syndrome (CTS) and other neural or trauma induced injuries or diseases affecting the hand.
2. Description of the Background
Repetitive motion disorders such as carpal tunnel syndrome are the most common occupational illnesses being reported among a wide range of professions which involve significant hand/wrist motions such as typists (particularly forceful typists) and meat cutters, etc. Carpal tunnel syndrome (CTS) symptoms include: decreased strength; paresthesias (burning or tingling) in the thumb and adjacent fingers; pain in the wrist, palm, forearm; decreased median nerve conduction velocities; and sensory loss in areas of the hand innervated by the median nerve.
Symptoms resembling CTS maybe due to chronic diseases such as rheumatoid arthritis or diabetes mellitus, congenital defects, acute trauma, age, birth control pill usage, and pregnancy. Historically, to aid in the diagnosis of the symptoms, Tinel's Sign, Phalen's Test, and electromyography nerve conduction tests are usually conducted. Additional tests have been developed to aid in symptom diagnosis which are based on specific measurable parameters such as: the expected weakness of the diseased hand; the decreased sensitivity of the fingers to applied vibrational stimulus; restricted range of motion; sensitivity to applied pressure; and chemical analysis of body proteins.
By lightly percussing the course of the median nerve for several seconds, a tingling sensation may be felt in the distribution of the median nerve, indicating a positive Tinel's Sign that suggests that CTS may be present. Phalen's Test generally requires the patient to press the backs of both hands together forming right angles, or holding the patient's wrist in acute flexion for 60 seconds. Numbness or tingling developing over the distribution of the median nerve is an indication that CTS is possible. Positive results in these tests are usually followed by electromyography (EMG) nerve conduction studies. An EMG is sensitive enough to detect the syndrome in 85% of those tested. However, a positive test result cannot be achieved in cases where the nerve has not been damaged to the extent that conduction has been impaired.
Presently, objective clinical information regarding the structure and functionality of the nervous system may be collected by recording electrical signals generated or propagated through the muscular or neural paths of interest. These electrodiagnostic tests require electrodes to be affixed to the patient under study so that electrical signals passing through the area of study may be collected and recorded. In general, these systems require the use of electrodes for both collection and stimulation, which may cause surface burns and/or pain to the patient during the evaluation. Two safety issues are present when using these tests: patient/practitioner contamination due to blood borne infection, and possible electrical shock. Both of these hazards may be minimized through disposable electrodes and through proper electrical shielding to make the systems "touch-proof" (shock-proof).
A number of devices, not relying on the art of electrodiagnostics, have been used to measure a variety of parameters which are intended to provide evidence of injury, specifically CTS. These devices fall into distinct categories which rely on different physical concepts or address specific symptoms. These groups are:
Muscle Strength: Device measures the strength of the finger(s), thumb, or the whole hand grip. PA1 Vibration Threshold: Device measures the threshold of the finger's sensitivity to applied vibrations. PA1 External Pressure: Device applies an external pressure to the appropriate nerve pathway and then asks for subjective report of numbness or weakness. PA1 Body Mobility: Device assesses range of motion in conjunction with EMG testing. PA1 Chemical Analysis: Body fluids are extracted and analyzed via electrophoresis or immunoassay to measure relative amounts ofproteins which may be used to infer injury.
For example, U.S. Pat. No. 4,774,966 relates to muscle strength measurement. This device is used to measure weakness present in the hand. If present, this weakness might be related to carpal tunnel syndrome and, as such, provide an early identification of the problem. The measurement is accomplished by measuring the strength of the intrinsic hand muscles innervated by the median nerve after it passes through the carpal tunnel. The motion of the hand is limited by the fixture provided such that only the muscles supplied by the median nerve are measured. The test allows screening by comparing the strength measured to a predefined normal strength. If the test individual should indicate weakness, further evaluation would be indicated. Weakness could be due to peripheral neuropathy, cerebral damage, cervical cord damage and neuromuscular disease.
U.S. Pat. No. 5,163,443 relates to muscle strength measurement. The applied forces exerted by the hand, wrist and forearm are measured with the intention of detecting the presence of cumulative trauma disorders, such as CTS. The forces measured are correlated with forces expected or required in specific work tasks, by comparing maximal strength as well as mobility of the limb in question. In addition, the system allows for grip and finger strength measurement. These measurements are made by a single transducer.
U.S. Pat. No. 5,471,996 relates to muscle strength measurement. The apparatus allows measurement of the muscle strength of the thumb to be studied. Assessment of the strength of the abductor pollicis brevis is important in the diagnosis of some types of neck and elbow injuries, and for CTS and other hand disorders. This apparatus restrains the hand and allows restricted movement to guarantee a reproducible force is applied by the thumb. Isometric and isokinetic testing is possible with this apparatus.
U.S. Pat. No. 5,002,065 relates to a vibration threshold measurement. Nerve injury may be induced by exposure to excessive vibration, causing the sensory threshold to be increased for the afflicted fingers. It has also been suggested that an increase in the perception threshold for vibration stimuli is the earliest detectable objective sign in patients with CTS. The patient's threshold to vibrational stimuli is measured and used to diagnose and screen for sensory disturbances due to conditions such as CTS. A normalized vibrational stimulus is applied to a finger of the patient. The frequency and amplitude of the stimulus are discrete and variable. As the test ensues and the frequency/amplitude are increased, the patient is requested to indicate the onset of sensory perception of the stimuli. The patient is also asked to indicate the loss of detection of the stimuli while the frequency/amplitude sweep is decreasing. Hand position, temperature, and uniform pressure are addressed during testing.
U.S. Pat. No. 5,230,345 relates to a vibration threshold measurement. CTS in a patient is detected by utilizing a vibratory waveform having a discrete frequency and a variable amplitude. The waveform is applied directly to the finger via contact with a speaker cone. A single finger is measured during the test procedure. When the stimuli is detected by the patient, the patient "clicks" the mouse which sends a control signal to the computer. This procedure is completed three times and the results averaged. The results are compared to a predetermined threshold baseline. Measurements exceeding the baseline indicate a diseased condition in the patient.
U.S. Pat. No. 5,301,683 relates to an external pressure measurement. Direct pressure applied for thirty seconds to the median nerve as it passes through the carpal tunnel at the base of the wrist. Patients having anatomic evidence of CTS will experience and report nu ness, pain, weakness orparesthesias in the distribution of the median nerve distal to the carpel tunnel. The applied pressure is controlled, so that repeatable tests may be accomplished.
U.S. Pat. No. 5,513,651 relates to a body mobility measurement combined with a surface electromyography test. A range of motion arm (ROMA) having six degrees of freedom is utilized to determine the range of motion in the upper and lower back while recording an exerting force on a strain gauge to simulate lifting conditions. This system allows a non-invasive, non-loading test for analyzing myofacial injuries and repetitive stress injuries. A protocol for evaluating the relationship between muscle groups is provided to determine if the problem is cervical, CTS or cubital tunnel.
U.S. Pat. No. 5,583,201 relates to a chemical analysis measurement useful for the diagnosis of peripheral nerve damage, including the damage which causes back and neck pain. A body fluid sample is extracted and subjected to a two-dimensional electrophoresis or an immunoassay. A diagnosis can be made by comparing the relative amounts of protein or proteins which increase or decrease in concentration to a standard control. This study determines whether the pain is caused by muscle or fibrous tissue injury.
The measurements described above relating to the strength of the muscles under study use predetermined standards of what is considered normal. The measurements are also limited to the muscle groups innervated by the median nerve. Since the hand also involves the ulnar nerve (fourth digit or ring finger and fifth digit or little finger), these measurements are not conclusive. Individual strength variations due to relative degree of muscle tone could also affect the results of these studies. The measurements relating to vibration sensitivity rely on the patient's compliance to provide an accurate threshold determination. The external pressure measurement described also relies on patient response. The mobility measurements described use EMG measurements in conjunction with the range of motion tests to remove the patient's subjective involvement. The chemical assay methodology described does not require the patient's compliance, but is invasive.